2 Power sources, 1 load, and possibly daisy chaining power

Thread Starter

SardyParty

Joined Jun 16, 2023
6
Hi,

I'm pretty new to all of this, so please let me know if something doesn't make sense.

I am building display units with LEDs in them, powered by a 5v USB C to make it easy to disconnect and cable manage. I would like to put a USB C port on the left side of the unit, as well as another USB C port on the right side, so that I can plug the power source into either side in order to light the LEDs. This is to make wire management easier since I don't know which side will be more direct, and if I want to eventually move them to a different location, I'd like to have the versatility.

My first question for this project is around safety. If there are two ports in the one circuit, what would happen if I accidentally plugged a power source into both ports? The little I know says that's not a good idea, so I've thought about putting a DPDT On-Off-On switch in the circuit. That way if the switch is flipped to the left then only the left USB port will allow power through the circuit, or if the switch is flipped to the right only the right USB port will allow power through the circuit. Something like this
Screenshot 2023-06-16 at 3.42.55 PM.png
If this isn't needed, or there's a better solution, please let me know.

The second part of this, is I actually want to build 4 identical display units in the same way, and I was wondering if it would be possible to daisy chain the power somehow. The idea would be that I could plug the power source into the first unit's – let's say – left USB port, then plug one end of a USB C cable into that same unit's right USB port, and the other end into the left USB port on the second unit. This would make it so much cleaner from a wire management standpoint, so this would be the preferred outcome if possible. I have no idea how to make this work along with making it safe in case two power sources are accidentally plugged into the circuit somewhere.

Thanks in advance for any help you can provide!
 

BobTPH

Joined Jun 5, 2013
8,653
My first question for this project is around safety. If there are two ports in the one circuit, what would happen if I accidentally plugged a power source into both ports?
I would not worry about this. If both are actually from the same source, there is no problem at all. If two different sources it might cause a problem if the voltages were significantly different, but that is not likely.
The second part of this, is I actually want to build 4 identical display units in the same way, and I was wondering if it would be possible to daisy chain the power somehow
Yes, you can daisy chain them. Just make sure the traces between the connectors are wide enough to carry the current for all four boards.
 

Thread Starter

SardyParty

Joined Jun 16, 2023
6
So just to make sure I’m fully understating, you’re saying that I can wire each unit with both USB C ports connected to the led circuit without a switch, and that would be fine if two separate power sources were plugged into one and that would also allow me to daisy chain the units as long as the wire/traces were thick enough for the current?
 

BobTPH

Joined Jun 5, 2013
8,653
No, I said it could be a problem if the voltages were different. The reason I would not bother to protect against it is that I consider an unlikely thing to do.
 

Thread Starter

SardyParty

Joined Jun 16, 2023
6
No, I said it could be a problem if the voltages were different. The reason I would not bother to protect against it is that I consider an unlikely thing to do.
Yes, sorry you did say that. Apologies for misquoting.

So as long as both sources are standard 5v USB C power adaptors, it should be ok since the voltages are the same? Would this be how that would be wired in order to allow for daisy chaining as well?
IMG_3064.jpeg
In the app I’m using to simulate the circuit it says the red PS is shorted. Might just be something wrong with the way the app simulates it, but that’s why I wanted to check.

I appreciate all your help!
 

BobTPH

Joined Jun 5, 2013
8,653
So as long as both sources are standard 5v USB C power adaptors, it should be ok since the voltages are the same?
No, two voltages are never exactly the same. But if close enough, like within 1/10 V, nothing will blow up. My question is why you would ever plug in two voltage sources?
 

Thread Starter

SardyParty

Joined Jun 16, 2023
6
No, two voltages are never exactly the same. But if close enough, like within 1/10 V, nothing will blow up. My question is why you would ever plug in two voltage sources?
I wouldn’t do it on purpose, it just could happen by accident for one reason or another. Not paying attention, someone who doesn’t know any better messing with it, I daisy chain them all together and then forget I plugged the first one into power already and I plug another one in on the other side of the last one. I’m just trying to fool proof it so I don’t break anything.
 

BobTPH

Joined Jun 5, 2013
8,653
If you put the switch as as proposed, you can no longer daisy chain them. Take your pick. Do whatever you want, I have given my opinion. Trying to convince me you are right serves no purpose, so I will bow out.
 

Thread Starter

SardyParty

Joined Jun 16, 2023
6
If you put the switch as as proposed, you can no longer daisy chain them. Take your pick. Do whatever you want, I have given my opinion. Trying to convince me you are right serves no purpose, so I will bow out.
I’m not trying to convince you I’m right, I’m just trying to make sure I understand. Sorry for asking questions in a forum.
 

ElectricSpidey

Joined Dec 2, 2017
2,756
If you can afford the voltage drop, perhaps a series diode in the line of both supplies can prevent the problem you are worried about.

You can compensate for the drop by changing the resistor values if necessary.
 
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